A hybrid automatic repeat request (HARQ) scheme is a combination of a forward error correction (FEC) scheme and an automatic repeat request (ARQ) scheme. In the HARQ scheme, it is determined whether an unrecoverable error is included in data received by a physical layer, and retransmission is requested upon detecting the error, thereby improving performance.
If the error is not detected from the received data, a receiver transmits a positive-acknowledgement (ACK) signal as a reception acknowledgement to report to a transmitter that reception is successful. If the error is detected from the received data, the receiver transmits a negative-acknowledgement (NACK) signal as the reception acknowledgement to report to the transmitter that the error is detected. The transmitter can retransmit the data upon receiving the NACK signal. The ACK signal or the NACK signal is called an ACK/NACK signal.
In a typical wireless communication system, only one carrier is considered even if a bandwidth between an uplink and a downlink is configured differently from each other. The carrier is defined with a center frequency and a bandwidth. A multiple carrier system uses a plurality of component carriers having a smaller bandwidth than a full bandwidth.
The multiple carrier system can support backward compatibility with respect to legacy systems, and significantly increases a data rate by using multiple carriers.
In order to perform HARQ in the multi-carrier system, it is necessary to consider transmission of an ACK/NACK signal. A plurality of transport blocks can be transmitted through multiple carriers. Resources for transmitting respective ACK/NACK signals for all of the plurality of transport blocks may not be fully ensured.